Why is this beach covered in giant snowballs?

Mother Nature has been gearing up for an epic snowball fight in Siberia.

Over the weekend, people along the Gulf of Ob woke up to find an 11-mile section of the beach covered with snowy spheres, some of which were as large as volleyballs. These snowballs, also called slob ice or sludge ice, formed as the ocean rose and slowly froze on the shore. When the water retreated, the ice remained, rolling over the wet sand and forming these natural snowballs.

That it was cold enough for the slob ice to form raises meteorological concerns about winter in North America. Siberia's snow levels are sometimes used to track the movements of the polar vortex, the weather phenomenon that pipes cold air into the U.S. According to the Daily Mail, the presence of the snowballs in Siberia indicates that the vortex is already on the move and earlier than expected. If that pattern continues, it could strike the U.S. by January.